Volpe, 38, had worked a 4 p.m.-to-midnight tour the night before, and had had trouble sleeping.

Clicking through the morning news on TV, Volpe came upon the image of a smoldering tower.

Having participated in rescue operations during the 1993 World Trade Center attacks, he said his instincts kicked in almost immediately.

"I just got in my car and drove down there," he said to ABC News.

As he drove, Volpe did what any good cop would do. He tried to prepare himself.

"You put through in your mind, you know, different things that could happen and how you [would] react to things," he said. "So that's basically what I was doing -- trying to prepare myself."

It was a useless exercise.

"You couldn't see your hands in front of your face," he said. "The air was so dark. There was soot that was, like, up to your knees."

He said he remembered walking by St. Paul's Chapel, one of the oldest buildings in New York and where President Washington prayed after his inauguration.

The chapel is surrounded by a cemetery with tombstones that date back to the 19th century.

"You couldn't even see the tombstones in there. The debris was piled so high," Volpe said. "It looked like a war zone."

Volpe, a self-proclaimed "gym rat" who said he had worked out six days a week before the Sept. 11 attacks, said he gave it his all -- until exhaustion literally overtook him.

"I actually remember going back to my car, and a [police] lieutenant was walking around and he looked at me and said, 'Detective, are you all right?'" Volpe said. "I'm like, 'Yeah, I'm fine.'"

"I just, I couldn't remember where I parked my car. That's how confused I was from everything that was going on," he said.

He returned and continued to work at ground zero, day after day.

"After the first couple days, I was coughing up blood and every time I sneezed, blood would come out of my nose," he said.

He was given a paper mask that he said later turned out to have been fitted with the wrong filter.

From ground zero, Volpe was moved to Staten Island's Fresh Kills landfill, where the debris from the towers was being hauled.

He described his haunting memories of his work there.

"Everybody would get on this bus, and you would drive up this mountain and you'd get to the top, and when you got to the top the only way I could describe it was like these three football fields, and they were all lit up with lights and stuff," he said.

"What they would do is they'd [get] like 10 [detectives] or 12 detectives, and they would assign them to each football field and what you would do is, these big grappler machines would pick up all this debris and … would spread it out in this field and then you'd walk out there with a rake or a pick or something and you'd dig through all this stuff."

"You'd have a 25-pound bucket with you and you were picking up actual human remains, throwing them in this bucket and at the end of the day you'd bring it to the FBI and drop it outside their trailer. And they'd do a DNA [test] on it and then they'd come with a big frontloader and plow all that stuff that you went through and then dump a whole bunch of other stuff."

"You'd do that for 12 hours."

Volpe participated in the recovery effort for five months. Then he went back to his work at the 41st Precinct in the Bronx.

In 2004, he began to notice that he was getting winded much more quickly than he used to.

He consulted a doctor, who told him he'd lost 53 percent of his kidney function.

He faces a future of dialysis, and with some luck, an eventual kidney transplant.

"I'm basically waiting," he said. "Today I am fine. … Tomorrow I could [have] kidney failure, and then it means dialysis until they completely fail and I need a transplant."

He said there's a five-year waiting list for a new kidney.

"There's no telling how much longer I will live."

"I actually asked an EPA [Environmental Protection Agency] guy and … he looked [to me] like he was going to the moon, dressed up," Volpe said. "And he had this meter in his hand and he's walking around with it and I went up to the guy and I said, 'What's wrong with this picture?'"

"I said, 'Look what you're wearing and look what I'm wearing. What's going on here?'" Volpe said. "And he just didn't even answer me, he just walked away."